The Stax Diffuse Field Equalizers are set up for specific phones, generally Lambdas. I believe at least one was made for either an SR3 or SR5, even though this does not show in the Stax History.
The Sigma frequency response is quite different from the Lambdas, arguably more like a DFE and if you were to add such an equalizer to a Sigma you would probably get too much low and mid frequencies. Of course I haven't tried this so I could be wrong.





























